Learn how to save Heirloom Celery Seeds:
Celery is self-fertile, inspect-pollinated biennial. It will cross with celeria or other celeries. In cold zones, choose your plants in the fall. Dig them out being careful not to harm the roots. Replant them in dirt in something you can keep in a root cellar, the above-ground part mulched with straw.
Replant in spring after last frost; trim rotted prats. In warm zones, plant for seed in July and transplant in January. Set out 2 feet apart because second-year growth get high an wide. Later come tiny white blooms; still later, brown seeds.
To avoid loss on the ground, shake the top heads (which mature seed first) into a bag once in a while. Cut and dry on cloth or paper.